SPIRAL PATTERN FORMATION IN A SIMPLE TWO-PHASE FLOW SYSTEM

A spiral pattern formation in a gas-liquid two phase flow is investigated experimentally. Bubbles are injected periodically into a liquid layer with a free surface and emerge one by one from the surface to exhibit regular arrangements. These arrangements are characterized by a constant angular shift in the direction of bubble radial motion after the emergence. A transition from the regime with a shift of 180 degrees to the regime of smaller angles is found. Observation of bubble behavior shows that the compaction among emerging elements (bubbles) plays an important role in the pattern formation, as in the development of regular leaf arrangement around a plant stem, the phyllotaxis. A theoretical model including the flow advection and the bubble-bubble interaction is developed to get deeper insights into the pattern generation. It is found the model reproduces different patterns and the transition between the two regimes.